1. Field of the Invention
The present invention relates to a method of and an apparatus for forming a lot in the process where objects are processed lot by lot such as batch processing, and particularly relates to a method of and an apparatus for forming a mixed lot by collecting objects of different kinds.
2. Description of Related Art
In a wafer process in producing semi-conductor product, for example, there is a process wherein a plurality of wafers are stored in a case like a cassette and processed lot by lot, such as processing before diffusion and processing for diffusion. Here, the lot is composed by collecting wafers of the same kind.
Incidentally, a recent trend in the production of semi-conductor is various kinds by small quantity. Therefore, there is a case where number of wafers of the same kind forming one lot does not meet the predetermined number, that is, the number of wafers to be stored in a cassette. Production by such lot is unusually inefficient and the cost increases. Thereupon, production is usually made by adding wafers of the same kind to a cassette to meet the number, and the surplus products are kept as a stock.
But, the stock is rarely ordered because of the trend of various kinds by small quantity of semi-conductor products, tending to be unnecessary stock. When the unnecessary stock is finally dumped, the maintenance cost until then is totally wasted, and it is added to the cost of products, resulting in a factor of the higher cost.